The present invention relates to a control valve for controlling the displacement of a variable displacement compressor in a refrigerant circuit of an air conditioner.
One type of such control valve includes a pressure sensing mechanism and an electromagnetic actuator. The pressure sensing mechanism detects the pressure at a pressure monitoring point located in the refrigerant circuit. A pressure sensing member is actuated based on changes of the pressure at the pressure monitoring point. Accordingly, a valve body is moved such that the displacement of the variable displacement compressor is changed to counteract the pressure changes. As a result, the pressure at the pressure monitoring point is maintained at a target level. The electromagnetic actuator changes the target level by changing electromagnetic force applied to the valve body in accordance with the level of electric current supplied from the outside.
FIG. 8 illustrates the structure of such an electromagnetic actuator 101. The electromagnetic actuator 101 includes an accommodation cylinder 102. A stator 103 and a plunger 104 are accommodated in the cylinder 102. A coil 105 is located about the cylinder 102. As electric current is supplied to the coil 105, electromagnetic force is generated between the stator 103 and the plunger 104. This moves the plunger 104. The movement of the plunger 104 is transmitted to a valve body (not shown) by a rod 106.
A flat inner surface 107 and a peripheral wall 108 are formed in the lower end of the stator 103, which faces the plunger 104. The inner circumferential surface of the peripheral wall 108 is referred to as an inclined surface 108a. The inner surface 107 is surrounded by the inclined surface 108a. The cross-section of the peripheral wall 108 defines an acute angle. The inner surface 107 and the peripheral wall 108 define a recess 109. A flat distal surface 110 and an annular inclined surface 111 are formed in an upper end of the plunger 104, which faces the plunger 104. The inclined surface 111 is formed at the periphery of the distal surface 110. The distal surface 110 and the inclined surface 111 define a frustum portion 112.
When the coil 105 receives a low electric current, the position of the valve body, which is coupled to the plunger 104, is unstable (this state will be described in the preferred embodiment section). This fluctuates the electromagnetic force as the distance between the plunger 104 and the stator 103 changes. The structure shown in FIG. 8 suppresses thus fluctuation. The structure also increases the maximum level of the electromagnetic force applied to the valve body by the electromagnetic actuator 101.
For example, suppose the stator 103 has a triangular cross-section and the plunger 104 is formed as a cone the shape of which corresponds to the stator 103 as schematically shown in FIG. 9(a). This structure suppresses changes of the shortest distance between the stator 103 and the plunger 104 when the plunger 104 is moved.
Therefore, as shown in the graph of FIG. 9(b), the electromagnetic force applied to the valve body by the actuator 101 is relatively gradually changed by changes of the position of the plunger 104. This stabilizes the position of the valve body when the coil 105 receives a low current. The shapes of the plunger 104 and the stator 103 in FIG. 8 are determined to obtain the effect of the structure shown in FIG. 9(a). Specifically, the frustum portion 112 (having the inclined surface 111) and the recess 109 (having the inclined surface 108a) face each other.
Also, suppose the entire lower surface of the stator 103 and the entire upper surface of the plunger 104 are flat as schematically shown in FIG. 10(a). In this structure, the magnetic flux is increased when the plunger 104 approaches the stator 103.
Therefore, as shown in the graph of FIG. 10(b), the maximum value of the electromagnetic force applied to the valve body by the actuator 101 is increased. This permits a target pressure level, which is used as a reference in the operation of the pressure sensing mechanism, to be set to a higher level. In other words, a certain level of the target pressure can be set by a smaller actuator 101. This reduces the size of the control valve. The shapes of the plunger 104 and the stator 103 in FIG. 8 are determined to obtain the effect of the structure shown in FIG. 10(a). Specifically, the frustum portion 112 having the flat distal surface 110 and the recess 109 having the flat inner surface 107 face each other.
However, in the prior art, the sizes and the shapes of the recess 109 of the stator 103 and the frustum portion 112 of the plunger 104 are not optimized. Thus, a sufficient effect cannot be obtained.
Accordingly, it is an objective of the present invention to provide a control valve for a variable displacement compressor that optimizes the shapes of parts of a plunger and a stator that face each other.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a control valve for changing the displacement of a compressor is provided. The control valve includes an accommodation cylinder, a coil located about the accommodation cylinder, a stator located in the accommodation cylinder, a plunger located in the accommodation cylinder, and a valve body coupled to the plunger. When electric current is supplied to the coil, electromagnetic force is generated between the stator and the plunger and the plunger moves relative to the stator in the accommodation cylinder, accordingly. When the plunger moves, the valve body moves accordingly and adjusts the opening degree of a valve hole. A flat surface and a peripheral wall surrounding the flat surface are formed in an end of one of the plunger and the stator that faces the other one of the plunger and the stator. The peripheral wall has a tapered cross-section with an inclined inner surface. The inclined inner surface and the flat surface define a recess. A frustum portion is formed in an end of the other one of the plunger and the stator that faces the recess. The frustum portion includes a flat distal surface and an annular inclined surface. The taper angle of the peripheral wall is equal to or less than twenty degrees. The diameter of the flat distal surface of the frustum portion is equal to or greater than eighty percent of the largest diameter of the annular inclined surface.
The present invention may also be applied to a compressor used in a refrigerant circuit of an air conditioner. The compressor includes a control chamber, a bleed passage, a supply passage, and a control valve. The compressor displacement is changed by adjusting the pressure in the control chamber. The bleed passage connects the control chamber to a suction pressure zone of the refrigerant circuit. The supply passage connects a discharge pressure zone of the refrigerant circuit to the control chamber. The control valve changes the displacement of a compressor. The control valve includes an accommodation cylinder, a coil located about the accommodation cylinder, a stator located in the accommodation cylinder, a plunger located in the accommodation cylinder, and a valve body coupled to the plunger. When electric current is supplied to the coil, electromagnetic force is generated between the stator and the plunger and the plunger moves relative to the stator in the accommodation cylinder, accordingly. When the plunger moves, the valve body moves accordingly and adjusts the opening degree of a valve hole. A flat surface and a peripheral wall surrounding the flat surface are formed in an end of one of the plunger and the stator that faces the other one of the plunger and the stator. The peripheral wall has a tapered cross-section with an inclined inner surface. The inclined inner surface and the flat surface define a recess. A frustum portion is formed in an end of the other one of the plunger and the stator that faces the recess. The frustum portion includes a flat distal surface and an annular inclined surface. The taper angle of the peripheral wall is equal to or less than twenty degrees. The diameter of the flat distal surface of the frustum portion is equal to or greater than eighty percent of the largest diameter of the annular inclined surface.